The present invention concerns a valve assembly for a pipeline, particularly (though not exclusively) for an undersea pipeline, e.g. for oil or gas.
A known type of valve has a body which has a through passage for connection in line in a pipeline, the body containing obturator means for controlling flow through the passage; and the body being openable for maintenance, which may involve removal of the obturator means. Thus our published British patent specification No. 2143929 (U.S. Ser. No. 632,843) discloses a ball valve in which the body provides a socket that receives a replaceable core unit containing the ball member and seals and bearings therefor. Less sophisticated valves may still allow access and removal of parts. Check valves are often inconvenient because the obturator elements (i.e. the check plates) are pivoted on axle pins that pass right through the body, so that removal of an element is difficult or impossible, particularly for a check valve installed in an undersea pipeline.
It is a general problem with underwater valves that when they are opened in situ, water floods into the pipeline. It may take weeks to flush it all out again after the valve has been reassembled.